public class CheckboxStandard {

    public CheckboxStandard(ApexPages.StandardController controller) {

    }

    String[] countries = new String[]{};

    public PageReference test() {
        return null;
    }
    public List<Account> getMyAccounts() {
         return [SELECT Id, Name, AccountNumber FROM Account];
              }
    public List<SelectOption> getItems() {
        List<SelectOption> options = new List<SelectOption>();
        options.add(new SelectOption('US','US'));
        options.add(new SelectOption('CANADA','Canada'));
        options.add(new SelectOption('MEXICO','Mexico'));

        return options;
    }

    public String[] getCountries() {
        return countries;
    }

    public void setCountries(String[] countries) {
        this.countries = countries;
    }
}